Thermal ablation using radiofrequency is a new, minimally invasive modality employed as an alternative to surgery in patients with benign thyroid nodules and recurrent thyroid cancers. The Task Force Committee of the Korean Society of Thyroid Radiology (KSThR) developed recommendations for the optimal use of radiofrequency ablation for thyroid tumors in 2012. As new meaningful evidences have accumulated, KSThR decided to revise the guidelines. The revised guideline is based on a comprehensive analysis of the current literature and expert consensus.
A new sulfonated side-chain grafting unit containing two or four sulfonic acid groups was synthesized using sulfonated 4-fluorobenzophenone (FBP) and 1,1-bis(4-hydroxyphenyl)-1,4-((4-fluorophenyl)thio)phenyl-2,2,2-trifluoroethane (3FBPT). A conventional aromatic nucleophilic substitution (S N Ar) was used for copolymerization of poly(arylene ether sulfone) containing a methoxy group. After converting the methoxy group to the reactive hydroxyl group, this functionalized copolymer was reacted to graft the sulfonated side chains to make the comb-shaped sulfonated poly(arylene ether sulfone) copolymers. All the polymers were characterized by 1 H NMR, thermogravimetric analysis (TGA), the water uptake, and proton and methanol transport for fuel cell applications. These comb-shaped sulfonated polymers had good properties as polyelectrolyte membrane materials. The comb-shaped copolymers with two or four sulfonic acid groups show high proton conductivity in the range of 34-147 and 63-125 mS/cm, respectively. The methanol permeabilities of these copolymers were in the range of 8.2 × 10 -7 -5.6 × 10 -8 cm 2 /s. A combination of high proton conductivities, low water uptake, and low methanol permeabilities for some of the comb-shaped copolymers indicated that they are good candidate materials for proton exchange membrane in fuel cell applications.
Perfluorosulfonic acids such as Nafion are industrial standard cation exchange ionomers for polymer electrolyte membrane fuel cells because of their high gas permeability, hydrophobicity, and inertness to electro-chemical reaction. In this research, pentamethylguanidinium functionalized, perfluorinated hydroxide conducting ionomers for alkaline membrane fuel cells were prepared and characterized. The alkaline stability of the ionomers largely depended on the adjacent group that connected the cation; Sulfone guanidinium functionalized ionomer degraded almost completely after soaking in 0.5 M NaOH at 80 °C for 24 h, while phenylguanidinium functionalized ionomer did not degrade under the same conditions for 72 h. Spectroscopic data and density functional theory calculation suggested that the stability of the phenylguanidinium ionomer was greatly improved by charge delocalization of the formed resonance structure. Alkaline membrane fuel cells using the resonance stabilized perfluorinated ionomer in the catalyst layers on quaternized polyphenylene membrane showed excellent performance (ca. maximum power density = 466 mW/cm 2 ) and promising stability (ca. Tafel slope degradation rate = 225 μV/dec h) at 80 °C under H 2 /air conditions.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.